Mild cognitive impairment (MCI) affects up to 22% of US older adults aged 65 and older. Research suggests that physicians may recommend less cardiovascular disease (CVD) treatment for older adults with MCI due to assumptions about their preferences. To delve into the disparity between patient preferences and physician assumptions in CVD treatment recommendations, we conducted a multi-site qualitative study to explore the underlying reasons for this discrepancy, providing insights into potential communication barriers and strategies to enhance patient-physician relationships. Employing a descriptive qualitative approach, we conducted interviews with 20 dyads, comprising older adults with MCI (n = 11) and normal cognition NC (n = 9), and their respective care partners. During these interviews, participants were prompted to reflect on physicians recommending fewer guideline-concordant CVD treatments to older adults with MCI than those with NC and physicians presuming that older adults with MCI desired less care or treatment in general than those with NC. We identified three primary themes: (1) Most participants had negative reactions to the data that physicians might undertreat patients with MCI for CVD; (2) Participants suggested that physicians may undertreat patients with MCI due to physician assumptions about treatment effectiveness, patient prognosis, value, and treatment adherence, and (3) Participants proposed that physicians may elicit less input from patients with MCI about treatments because of negative physician assumptions about patient decision-making capacity and physician time limitations. This study underscores the pressing need for person-centered communication and involvement of older adults with MCI and their care partners in the decision-making process to ensure that decisions are well-informed, reflecting patients' genuine preferences and values. Addressing these concerns has the potential to substantially enhance the quality of care and treatment outcomes for this vulnerable population, ultimately promoting their overall well-being.